Genome-wide analysis of MYB family in Nicotiana benthamiana and the functional role of the key members in resistance to Bemisia tabaci.

MYB transcription factors (TFs) play a key role in plant resistance to abiotic and biotical stresses. However, little is currently known about their involvement in the plant defense to piercing-sucking insects. Here, we studied the MYB TFs that responded to and resisted Bemisia tabaci whitefly in the model plant Nicotiana benthamiana. Firstly, a total of 453 NbMYB TFs in N. benthamiana genome were identified and 182 R2R3-MYB TFs were analyzed for molecular characteristics, phylogenetic analysis, genetic structure, motif composition, and cis-elements. Then, six stress-related NbMYB genes were selected for further study. The expression pattern shows they were highly expressed in mature leaves and intensively induced upon whitefly attack. Combined with bioinformatic analysis, overexpression, ß-Glucuronidase (GUS) assay, and virus-induced silencing tests, we determined the transcriptional regulation of these NbMYBs on the genes in lignin biosynthesis and SA-signaling pathways. Meanwhile, we tested the performance of whitefly on plants with increased or silenced NbMYB genes expression and found that NbMYB42, NbMYB107, NbMYB163, and NbMYB423 were resistant to whitefly. Our results contribute to a comprehensive understanding of the MYB TFs in N. benthamiana. Furthermore, our findings will facilitate further studies on the role of MYB TFs in the interaction between plants and piercing-sucking insects.

Manipulation of Whitefly Behavior by Plant Viruses.

Whiteflies of the Bemisia tabaci complex transmit hundreds of plant viruses belonging to the genera Begomovirus and Crinivirus, among others. Tripartite interactions of whitefly-virus-plant frequently occur during virus infection and transmission. Specifically, virus transmission-related behavior of whitefly, such as preference and feeding, may be altered by viruses and thus exert significant impacts on the outcome of virus spread and epidemics. Here, we provide an overview on the current understanding of the manipulation of whitefly behavior by plant viruses. Plant viruses can significantly modulate whitefly preference and feeding behavior, either directly or in a plant-mediated manner. In general, non-viruliferous whiteflies tend to prefer virus-infected plants, and viruliferous whiteflies are more likely to prefer uninfected plants. In most cases, virus infection of plants and/or whitefly seems to exhibit positive or no effects on whitefly feeding on plants. The significance and evolution of these patterns are then discussed. Finally, we suggest several future directions of research, such as the exploration of temporal dynamics and the dissection of underlying mechanisms of virus-induced changes in whitefly behavior.

Development of a one-step immunocapture real-time RT-PCR assay for detection of tobacco mosaic virus in soil.

Tobacco mosaic virus (TMV) causes significant losses in many economically important crops. Contaminated soils may play roles as reservoirs and sources of transmission for TMV. In this study we report the development of an immunocapture real-time RT-PCR (IC-real-time RT-PCR) assay for direct detection of TMV in soils without RNA isolation. A series of TMV infected leaf sap dilutions of 1:101, 1:102, 1:103, 1:104, 1:105 and 1:106 (w/v, g/mL) were added to one gram of soil. The reactivity of DAS-ELISA and conventional RT-PCR was in the range of 1:102 and 1:103 dilution in TMV-infested soils, respectively. Meanwhile, the detection limit of IC-real-time RT-PCR sensitivity was up to 1:106 dilution. However, in plant sap infected by TMV, both IC-real-time RT-PCR and real-time RT-PCR were up to 1:106 dilution, DAS-ELISA could detect at least 1:103 dilution. IC-real-time RT-PCR method can use either plant sample extracts or cultivated soils, and show higher sensitivity than RT-PCR and DAS-ELISA for detection of TMV in soils. Therefore, the proposed IC-real-time RT-PCR assay provides an alternative for quick and very sensitive detection of TMV in soils, with the advantage of not requiring a concentration or RNA purification steps while still allowing detection of TMV for disease control.

Genetic diversity and population structure of rice stripe virus in China.

Rice stripe virus (RSV) is one of the most economically important pathogens of rice and is repeatedly epidemic in China, Japan and Korea. The most recent outbreak of RSV in eastern China in 2000 caused significant losses and raised serious concerns. In this paper, we provide a genotyping profile of RSV field isolates and describe the population structure of RSV in China, based on the nucleotide sequences of isolates collected from different geographical regions during 1997-2004. RSV isolates could be divided into two or three subtypes, depending on which gene was analysed. The genetic distances between subtypes range from 0.050 to 0.067. The population from eastern China is composed only of subtype I/IB isolates. In contrast, the population from Yunnan province (southwest China) is composed mainly of subtype II isolates, but also contains a small proportion of subtype I/IB isolates and subtype IA isolates. However, subpopulations collected from different districts in eastern China or Yunnan province are not genetically differentiated and show frequent gene flow. RSV genes were found to be under strong negative selection. Our data suggest that the most recent outbreak of RSV in eastern China was not due to the invasion of new RSV subtype(s). The evolutionary processes contributing to the observed genetic diversity and population structure are discussed.